Numerous engine designs have been proposed over the years for achieving various performance characteristics. The most familiar design is the slider crank reciprocating piston internal combustion engine. In the slider crank engine a connecting rod connects the piston(s) to the offset crankpins of a crankshaft to translate the linear reciprocating motion of the pistons to rotary motion. While the slider crank design has proven to have great utility, it does have certain disadvantages and limitations, e,g., the number and weight of engine parts, size, and power loss due to friction associated with side loading of pistons, as well as pumping losses. The slider crank also has limitations as to volumetric efficiency arising from the fixed cycle dynamics of the slider crank engine, wherein the Top Dead Center (TDC) position of the crankshaft invariably corresponds to Top Piston Position (TPP) in the cylinder and the Bottom Dead Center (BDC) position corresponds to Bottom Piston Position (BPP).
Of course, the cycle dynamics of an engine (piston position and velocity/cylinder volume and rate of volume change as a function of crankshaft position) has a direct effect upon the thermodynamics of the engine (pressure/temperature and rate of change thereof) which has a direct effect upon the chemical reactions driving the engine (exothermic oxidation of fuel). Each of the foregoing determine the efficiency of the engine and the nature of the exhausted end products of combustion.
A variety of expedients for improving the slider crank engine have been considered over the years, including devices for altering the cycle dynamics of the engine. For example, the following devices have been proposed: pistons with variable compression height, see U.S. Pat. No. 4,979,427, connecting rods with variable length, see U.S. Pat. No. 4,370,901; connecting rods with a pair of wrist pins one of which is connected to an internal slider and the second of which traverses an arcuate slot, see U.S. Pat. No. 4,463,710; and supplemental pistons and cylinders converging into a shared combustion chamber, see U.S. Pat. No. 3,961,607. Each of these devices results in a more complex engine having more parts and greater reciprocating and total mass.
A more common expedient for overcoming volumetric inefficiency and to provide an optimal fuel air mixture at high RPMs is the air intake compressor. A variety of compressor types have been suggested in the past. Of these, the supercharger, e.g., Root's type, and the turbo charger are the most common. Compressors of this type are discrete pump units fitted to an engine and driven at a selected ratio of compressor shaft speed to engine shaft speed. In the case of the turbo charger, the compressor is driven by a turbine positioned in the engine exhaust stream and thus has no mechanical connection to the engine crank, leading to "turbo lag". Due to the high RPMs and close tolerances required by turbo chargers and superchargers to develop pressure boost, these accessories are generally expensive and degrade prior to the engine upon which they are installed. For these reasons they are sometimes considered appropriate only for exotic or performance applications.
The scotch yoke has also been employed in certain engine designs seeking improved cycle dynamics over the slider crank engine. For example, see U.S. Pat. Nos. 4,584,972, 4,887,560, 4,485,768 and 4,803,890. While these efforts certainly must be considered creative, they either utilize a great number of parts in a complex arrangement or are plagued by certain weaknesses encountered in the traditional scotch yoke design, such as unacceptable wear and tear at the crank/slot interface. Furthermore, the benefits of changes in cycle dynamics are limited because more than one stroke of a cycle must be provided for, i.e., intake, compression, power and exhaust, each stroke having different optimal cycle dynamics.
The present application then seeks to describe a new and novel engine having improved cycle dynamics which employs a scotch yoke motion translator. The engine is also capable of developing a more optimal fuel/air over a wider range of operating speeds thereby providing a more efficient engine with a higher power to weight ratio, reduced pumping losses and reduced pollution emissions.